Neuroscientists from the Department of Economics wanted to try and explain why this might be. In new research, published in Nature Human Behaviour, the team looked at the different areas of the brain that are active when decisions about sharing are made.

In a series of experiments, male and female participants were asked to imagine 100 people ranging from 1 (their closest friend) to 100 (a random stranger on the street). They chose whether to share money with people at social levels 1, 5, 10, 20, 50 and 100, or to keep it for themselves.

In one of the experiments in the study, the participants were also given a drug called Amisulpride, which inhibited the brain's reward system. The researchers believed this drug would suppress how much value the subjects thought the rewards had, either selfish or prosocial (sharing).

An area right in the middle of the brain called the striatum is active whenever a decision is made. In the experiment without Amisulpride, the striatum was more strongly activated in female brains when they shared rather than when they were selfish. The opposite was true for men. In other words, women's reward systems were more sensitive to sharing, and men's more sensitive to being selfish.

In the drug inhibitor experiment, sharing behaviour in women and selfishness in men were both reduced.

"We expected to find the effect for women, because we knew from behavioural studies that women are often more prosocial then men," Alexander Soutschek, a psychologist at the University of Zurich and lead author of the study, told Business Insider. "We expected that the effect in men might be smaller than in women, but we did not expect that the effect was in the opposite direction."

Although the research showed there were differences between men and women at a biological level, Soutschek said they didn't draw any conclusions about why these differences exist.

"It would be a fallacy to believe that differences in brain functioning must be innate or have an evolutionary basis," he said. "In contrast, the dopaminergic system is crucial for learning, and this fits with the idea that the observed differences might be the product of gender stereotypes in western societies. However, as I said, this just appears to be the best explanation for us, we cannot rule out the evolution hypothesis."